1. Field of the Invention
The present invention relates to a failure detecting device for supercharging-pressure control means in a supercharging device of an engine, the supercharging device comprising: a turbocharger for supercharging the engine; supercharging-pressure control means for controlling a supercharging pressure in a supercharging intake air passage downstream of the turbocharger; engine-load detecting means for detecting an engine load; and supercharging-pressure detecting means for detecting the supercharging pressure in the supercharging intake air passage.
2. Description of Related Art
Japanese Patent Application Laid-open No. 2003-120304 discloses a device which determines abnormality of the turbocharger by comparing a reference supercharging pressure preset corresponding to an engine load with an actual supercharging pressure detected by a supercharging pressure sensor, when a nozzle vane for controlling a supercharging pressure generated by a turbocharger of an engine is in a maximum or minimum opening-degree position and the engine is in a low-rotational-speed low-load region or a high-rotational-speed high-load region.
In the conventional turbocharger, there is recognized a time lag (so-called turbo-lag) between the reference supercharging pressure preset according to the engine load and the actual supercharging pressure detected by the supercharging pressure sensor. Therefore, as in the above-described conventional device, a device that determines a failure of the turbocharger on the basis of the comparison between the reference supercharging pressure and the actual supercharging pressure has a possibility to erroneously determine that the turbocharger has failed although the turbocharger is normal, when the engine load suddenly changes to cause a time lag in the response of the actual supercharging pressure which leads to a difference between the reference supercharging pressure and the actual supercharging pressure.